This invention relates to alarm annunciators to be used for instance, with electric power transformers. More specifically, the present invention is a low-cost alarm annunciator which allows identification and disablement of alarm signals in a substation transformer.
Transformers are used throughout electric power distribution networks. Substation transformers are large transformers found at distribution substations and are important as a link in the distribution of electric power from main power transmission lines to lines which distribute power to customers in a local area. Consequently, it is understood that the monitoring of the operating characteristics of such transformers is part of assuring a reliable system.
Therefore, there are normally a number of sensors and associated alarms which identify various alarm conditions for a transformer. These alarms can be characterized as either critical or non-critical dependent on the particular set of circumstances. Generally, alarms such as the transformer oil temperature alarm, the winding temperature alarm, the low oil level alarm, the pressure relief alarm, the loss of oil pump alarm, and the tank high pressure alarm are considered critical. Non-critical alarms include the cylinder pressure alarm and the low tank pressure alarm.
Typically, all of the alarms for a particular transformer are bussed together and sent as one signal into a control house of a substation for display and into a supervisory remote computer system for transmission to a central office for many substations. Such a single transformer alarm does not identify the type of alarm condition. The use of an annunciator at the transformer identifies the particular alarm so that the onsite operator may tell which alarms are present. The annunciator allows an individual alarm signal to be isolated from the transformer alarm. In this way, the transformer may remain in service, if desired, and the occurrence of another alarm may be monitored away from the transformer.
Prior art annunciators are unduly expensive and complex. Furthermore, they rely on an independent power supply which may itself be subject to failure. Also, the voltage level in prior art annunciators is much more critical and failure due to power surges or lightning may inhibit sending alarm signals.